Can't use BinarySecurityToken and Secret Generated

Clearance and Reporting
1

Iam using dotnet 4.5 to integrating with Zatca as below, and iam still on developer edition:
1- i used CsrGenerator to get CSR value, then send it to:
https://gw-fatoora.zatca.gov.sa/e-invoicing/developer-portal/compliance
to get BinarySecurityToken and secret
2- use BinarySecurityToeken + “:” + secret, and convert tobase64String, and add "Basic " at start.
i always received 401 error on (https://gw-fatoora.zatca.gov.sa/e-invoicing/developer-portal/invoices/reporting/single)
But when i used cert4sign website, and send to it the same data used for generate CSR, it returns valid credentials, and i can use it.
I need to know:
1- Why i getting 401 if i generate CSR from my side?
2- Every time i need to send invoice, i need to generate CSR, certificate, Private key?
or i can generate all these value at once, and use it every time i need to send invoice.

Sorry for the length, and thank you for your effort.

3

Thanks Malik, it was very helpful to me
I understand now that in sandbox i use fixed credentials, but in Simulation, and production, generated credentials from my code should be works properly.
Thanks again, your efforts is much appreciated.